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Martensitic stainless steel have the highest strength but also the lowest corrosion resistance of the stainless steel. Martensitic steels with high carbon contents are used for tool steel. Due to their high strength in combination with somecorrosion resistance, martensitic steels are suitable for applications where the material is subjected to both corrosion and wear. An example is in hydroelectric turbines.  Martensitic grades of stainless steel were developed in order to provide a group of stainless alloys that would be corrosion resistant and hardenable by heat treating. The martensitic grades are straight chromium steels containing no nickel. They are magnetic and can be hardened by heat treating. The martensitic grades are mainly used where hardness, strength, and wear resistance are required. Martensitic stainless steel has a relatively high carbon content (0.1% – 1.2%) compared to other stainless steel. The martensitic steels are plain chromium steel containing between 12% and 18% chromium, can be heat treated to obtain high strength with good ductility. Martensitic stainless steel has very high hardenability. When only limited corrosion resistance or resistance to moderately elevated temperature scaling is required, can be used in the annealed condition, but its highest corrosion resistance is attained in the hardened and stress relieving (low temperature tempered) condition. Type 410 Basic martensitic grade, containing the lowest alloy content of the three basic stainless steels (304, 430, and 410). Low cost, general purpose, heat treatable stainless steel. Used widely where corrosion is not severe (air, water, some chemicals, and food acids. Typical applications include highly stressed parts needing the combination of strength and corrosion resistance such as fasteners. Type 410S Contains lower carbon than Type 410, offers improved weldability but lower hardenability. Type 410S is a general purpose corrosion and heat resisting chromium steel recommended for corrosion resisting applications. Type 414 Has nickel added (2%) for improved corrosion resistance. Typical applications include springs and cutlery. Type 416 Contains added phosphorus and sulfur for improved machinability. Typical applications include screw machine parts. Type 420 Contains increased carbon to improve mechanical properties. Typical applications include surgical instruments. Type 431 Contains increased chromium for greater corrosion resistance and good mechanical properties. Typical applications include high strength parts such as valves and pumps. Type 440 Further increases chromium and carbon to improve toughness and corrosion resistance. Typical applications include instruments. The major alloying addition in martensitic stainless steel is chromium in the range of 11 to 17%. The carbon levels can vary from 0.10 to 0.65% in these alloys. This radically changes the behavior of the martensitic alloys relative to the ferritic 400 Series alloys. The high carbon enables the material to be hardened by heating to a high temperature, followed by rapid cooling (quenching). Martensitic types offer a good combination of corrosion resistance and superior mechanical properties, as produced by heat treatment to develop maximum hardness, strength and resistance to abrasion and erosion. The martensitic grades are usually sold in the soft state. This allows the customers to cut or form the parts before they are thermally hardened. End uses include cutlery, scissors, surgical instruments, wear plates, garbage disposal shredder lugs, and industrial knives. The AL 403 alloy is used to make vanes for steam turbines. Stainless Steel – MartensiticAlloy (UNS Designation) End UseComposition nominal wt%SpecificationsDensity lb/in3 (g/cm3)Tensile Strength ksi. (MPa)0.2% Yield Strength ksi. (MPa)Elong- ation %HardnessAL 403 S40300 Turbine blades, banding, strapping and hose clampsC 0.15 max, Mn 1.0 max, Si 0.5 max, Cr 11.5-13.0, Ni 0.6 max, P 0.04 max, S 0.03 max, Fe BalanceASTM A176 AMS QQ57630.280 (7.75)70 min (485 min)30 min (205 min)25 min96 Rockwell B max Source: wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

cold working and heat treatment conditions chemical composition effects Cold Working and Heat Treatment Cold working of austenitic stainless steel can partially transform austenitic to martensitic. As martensitic stainless steel is ferromagnetic, cold working austenitic stainless steel can show a degree of ‘pull’ towards a magnet. This usually occurs at sharp corners, sheared edges or machined surface but can be detected on wrought products such as rods or bars which may have been cold straightened, following the final hot rolling or annealing in the mill. The degree to which this occurs depends on the compositional effects of austenitic stabilising elements. High nickel or nitrogen bearing grades tolerate more cold working before localised increases in permeability are noticed. These increases in permeability can be reversed by full solution annealing at temperatures around 1050 / 1120C with rapid cooling. This transforms any cold-formed martensitic to austenitic, the non-magnetic phase, which is then retained on cooling. The best austenitic stainless steel types for low permeability applications are those with high austenitic stability as these have low permeability in both annealing or cold working conditions. These include the nitrogen bearing types, 304LN (1.4311) and 316LN 1.4406 or the high nickel types such as 310 1.4845.

Duplex Stainless Steel Group is intermediate in terms of structure and alloy content between ferritic and austenitic stainless steel. The main characteristic that differentiates Austenitic-ferritic steel from austenitic and ferritic stainless steel is that they have a higher yield strength and tensile strength. They are therefore often used in dynamically stressed machine parts, e.g. suction rolls for paper machines. New areas of application are within the oil, gas and petrochemical sector, seawater bearing systems and the offshore industry. Duplex Stainless Steels are normally named Duplex stainless steel pipes due to the two phases present in the microstructure. Typically twice the yield of austenitic stainless steel. Minimum Specified Ultimate Tensile Strength typically 680 to 750N/mm2 (98.6 to 108ksi).  Elongation typically > 25%. Superior corrosion resistance than a 316. Good Resistance to stress corrosion cracking in a chloride environment. Duplex stainless steel materials have improved over the last decade; further additions of Nitrogen have been made improving weldability. Because of the complex nature of this material it is important that sourced from good quality steel mills and is properly solution annealing. Casting and possibly thick sections may not cool fast when annealing causing sigma and other deleterious phases to form. The material work hardens if cold formed; even the strain produced from welding can work harden the material particularly in multi pass welding.  Therefore a full solution anneal is advantageous, particularly if low service temperatures are foreseen. The high strength of this material can make joint fit up difficult. Usable temperature range restricted to, -50 to 280°C Used in Oil & Natural Gas production, chemical plants etc. The microstructure shows an image of a duplex stainless steel pipes Metallographic Test – Metallography Testing Metallographic Test Report Standard Duplex Stainless Steel S31803 22Cr 5Ni 2.8Mo 0.15N PREN = 32-33 Super Duplex Stainless Steel:   Stronger and more corrosion resistant than standard duplex stainless steel.  S32750(Zeron 100) 25Cr 7.5Ni 3.5Mo 0.23N  PREN = 40 Duplex stainless steel solidifies initially as ferrite, then transforms on further cooling to a matrix of ferrite and austenite.  In modern raw material the balance should be 50/50 for optimum corrosion resistance, particularly resistance to stress corrosion cracking.  However the materials strength is not significantly effected by the ferrite / austenite phase balance. The main problem with duplex stainless steel is that it very easily forms brittle intermetalic phases, such as Sigma, Chi and Alpha Prime.  These phases can form rapidly, typically 100 seconds at 900°C.  However shorter exposure has been known to cause a drop in toughness, this has been attribute to the formation of sigma on a microscopic scale.   Prolonged heating in the range 350 to 550°C can cause 475°C temper embrittlement.   For this reason the maximum recommended service temperature for suplex stainless steel is about 280°C. Sigma (55Fe 45Cr) can be a major problem when welding thin walled small bore pipes made of super duplex stainless steel, although it can occur in thicker sections.  It tends to be found in the bulk of the material rather than at the surface, therefore it probably has more effect on toughness than corrosion resistance.  Sigma can also occur in thick sections, such as castings that have not been properly solution annealed (Not cooled fast enough). However most standards accept that deleterious phases, such as sigma, chi and laves, may be tolerated if the strength and corrosion resistance are satisfactory. Nitrogen is a strong austenite former and largely responsible for the balance between ferrite and austenite phases and the materials superior corrosion resistance.  Nitrogen can’t be added to filler metal, as it does not transfer across the arc. It can also be lost from molten parent metal during welding.  Its loss can lead to high ferrite and reduced corrosion resistance.  Nitrogen can be added to the shielding gas and backing gas, Up to about 10%; however this makes welding difficult as it can cause porosity and contamination of the Tungsten electrode unless the correct welding technique is used.  Too much Nitrogen will form a layer of Austenite on the weld surface.  In my experience most duplex stainless steel and super duplex stainless steel are TIG welded using pure argon. Backing / purge gas should contain less than 25ppm Oxygen for optimum corrosion resistance. Fast cooling from molten will promote the formation of ferrite, slow cooling will promote austenite. During welding fast cooling is most likely, therefore welding consumables usually contain up to 2 – 4% extra Nickel to promote austenite formation in the weld.  Duplex stainless steel should never be welded without filler metal, as this will promote excessive ferrite, unless the welded component is solution annealed. Acceptable phase balance is usually 30 – 70% Ferrite Duplex welding consumables are suitable for joining duplex to austenitic< stainless steel or carbon steel; they can also be used for corrosion resistant overlays.  Nickel based welding consumables can be used but the weld strength will not be as good as the parent metal, particularly on super duplex stainless steel. Low levels of austenite – Poor toughness and general corrosion resistance. High levels of austenite: – Some Reduction in strength and reduced resistance to stress corrosion cracking. Good impact test results are a good indication that the material has been successfully welded.  The parent metal usually exceeds  200J.  The ductile to brittle transition temperature is about –50°C. The transition is not as steep as that of carbon steel and depends on the welding process used. Flux protected processes, such as MMA; tend to have a steeper transition curve and lower toughness.  Multi run welds tend to promote austenite and thus exhibit higher toughness Tight controls and the use of arc monitors are recommended during welding and automatic or mechanised welding is preferred.  Repair welding can seriously affect corrosion resistance and toughness; therefore any repairs should follow specially developed procedures.  See BS4515 Part 2 for details. Production control test plates are recommended for all critical poduction welds. Welding procedures should be supplemented by additional tests, depending on the application and the requirements of any application code:- A ferrite count using a Ferro scope is probably the most popular.  For best accuracy the ferrite count should be performed manually and include a check for deleterious phases. Good impact test results are also a good indication of a successful welding procedure and are mandatory in BS4515 Part 2. A corrosion test, such as the G48 test, is highly recommended. The test may not model the exact service corrosion environment, but gives a good qualative assessment of the welds general corrosion resistance; this gives a good indication that the welding method is satisfactory. G48 test temperature for standard duplex stainless steel is typically 22°C, for super duplex stainless steel 35°C Typical Welding Procedure For Zeron 100 (Super duplex stainless steel) Super duplex stainless steel pipes 60mm Od x 4mm Thick     Position 6G Maximum Interpass 100°C     Temperature at the end of welding < 250°C 1.6mm Filler Wire          85 amps  2 weld runs (Root and Cap) Arc energy  1 to 1,5 KJ/mm         Travel speed  0.75 to 1 mm/sec Recommended Testing Ferric Chloride Pitting Test To ASTM G48 : Method A Chemical analysis of root Ferrite count Duplex Stainless Steels have a structure that contains both ferrite and austenite. Duplex alloys have higher strength and better stress corrosion cracking resistance than most austenitic alloys and greater toughness than ferritic alloys, especially at low temperatures. The corrosion resistance of duplex alloys depends primarily on their composition, especially the amount of chromium, molybdenum, and nitrogen they contain. Duplex alloys are often pided into three sub-classes: Lean Duplex (ATI 2102 duplex, ATI 2003 duplex, and ATI 2304 duplex alloys), Standard Duplex (ATI 2205� duplex alloy), and Superduplex (ATI 255 duplex and UNS S32760 duplex alloys). Duplex Stainless SteelAlloy (UNS Designation) End UseComposition nominal wt%SpecificationsDensity lb/in3 (g/cm3)Tensile Strength ksi. (MPa)0.2% Yield Strength ksi. (MPa)Elong- ation %HardnessS82011 Piping and tubing in general corrosion and chloride environments, structural components, storage tanks.C 0.03 max, Mn 2.0-3.0, Si 1.0 max, Cr 20.5-23.5, Ni 1.0-2.0, Mo 0.10-1.00, N 0.15-0.27, Fe BalanceASTM A2400.279 (7.75)101 min (sheet) / 95 min (plate) (700 min (sheet) / 655 min (plate))75 min (sheet) / 65 min (plate) (515 min (sheet) / 450 min (plate))30 min31 Rockwell C maxS32003 Piping, tubing in general corrosion and choride environments, architectural structures, roofing, topside applications on oil platformsC 0.03 max, Mn 2.0 max, Si 1.0 max, Cr 19.5-22.5, Ni 3.0-4.0, Mo 1.5-2.0, N 0.14-0.2, Fe BalanceASTM A240 ASME Code Case 25030.279 (7.72)100 min (sheet) / 95 min (plate) (690min (sheet) / 655 min (plate)70 min (sheet) / 65 min (plate) (485 min (sheet) / 450 min (plate)25 min31 Rockwell C max2304 S32304 Tanks, digesters, pressure vessels, pipesC 0.03 max, Mn 2.50 max, Si 1.0 max, Cr 21.5-24.5, Ni 3.0-5.5, Mo 0.05-0.60, Cu 0.05-0.60, N 0.05-0.20, Fe BalanceASTM A240, ASME SA-240, SAE J4050.280 (7.8)87 min (600 min)58 min (400 min)25 min32 Rockwell C max2205 S31803/S32205 Duplex stainless steel Pipes, Tubing in general corrosion and chloride stress corrosion environmentsC 0.03 max, Mn 2.0 max,Si 1.0 max, Ni 4.5-6.5, S31803: Cr 21.0-23.0, Mo 2.5-3.5, N 0.08-0.20, S32205: Cr 22.0-23.0, Mo 3.0-3.5, N 0.14-0.20, Fe BalanceASTM A240 ASME SA-2400.283 (7.82)90 min (31803) / 95 min (32205) (620 min (31803) / 655 min (32205))65 min (450 min)25 min31RockwellC max2507 S32750 Super duplex stainless steel pipes, containers for CPI, Oil & GasC 0.04 max, Mn 1.5 max, P 0.04 max, S 0.03 max, Si 1.0 max, Cr 24.0-27.0, Ni 4.5-6.5, Mo 2.9-3.9, N 0.1-0.25, Cu 1.5-2.5, Fe BalanceASTM A2400.279 (7.73)110 min (760 min)80 min (550 min

To understand how duplex stainless steel works, first compare the composition of two familiar steel austenitic 304 (1.4301) and ferritic 430 (1.4016). StructureGrade EN NumberCSiMnPSNCr  NiMoFerritic4301.40160.081.001.000.0400.015–16.0/18.0––Austenitic3041.43010.071.002.000.0450.0150.1117.5/19.58.0/10.5– The important elements in stainless steel can be classified into ferritisers and austenitisers. Each element favours one structure or the other:  Ferritisers – Cr (chromium), Si (silicon), Mo (molybdenum), W (tungsten), Ti (titanium), Nb (niobium)  Austenitisers – C (carbon), Ni (nickel), Mn (manganese), N (nitrogen), Cu (copper)  Grade stainless steel 430 has a predominance of ferritisers and so is ferritic in structure. Grade stainless steel 304 becomes austenitic mainly through the use of about 8% nickel. To arrive at a duplex structure with about 50% of each phase, there has to be a balance between the austenitisers and the ferritisers. This explains why the nickel content of duplex stainless steels is generally lower than for austenitics. Here are some typical compositions of duplex stainless steel: Grade EN No/UNSTypeApprox Composition  CrNiMoNMnWCuLDX21011.4162/  S32101 Lean21.5 1.50.30.225––DX22021.4062/ S32202Lean232.50.30.2–––RDN 9031.4482/  S32001Lean201.80.2 0.114.2––23041.4362/  S32304 Lean234.8 0.3 0.10–––22051.4462/  S31803/ S32205Standard 225.73.10.17–––25071.4410/  S32750Super25740.27–––Zeron 1001.4501/  S32760Super25 73.20.25–0.70.7Ferrinox 255/  Uranus 2507Cu1.4507/  S32520/ S32550Super256.53.50.25––1.5 In some of the recently developed stainless steel grades, nitrogen and manganese are used together to bring the nickel content to very low levels. This has a beneficial effect on price stability.  At present, we are still very much in the development phase of duplex stainless steel. Therefore, each mill is promoting its own particular brand. It is generally agreed that there are too many grades. However, this is likely to continue until the “winners” emerge. Established in 2008, wilsonpipeline Pipe Industry Co., Limited is a professional organizer and one-stop-shop supplier for steel piping system products, including duplex stainless steel pipes and duplex stainless steel tubes, duplex stainless steel flangesand duplex stainless steel fittings, duplex stainless steel butt-welding pipe fittings, duplex stainless steel elbows, duplex stainless steel tees, duplex stainless steel reducers, duplex stainless steel stub end, duplex stainless steel gaskets, duplex stainless steel fasteners, duplex stainless steel valves, duplex stainless steel Sanitary Services etc. in China. We have devoted to providing the best solutions of steel materials and industrial equipment for our respected customers.

The idea of duplex stainless steel dates back to the 1920s with the first cast being made at Avesta in Sweden in 1930. However, it is only in the last 30 years that duplex stainless steel have begun to “take off” in a significant way. This is mainly due to advances in steelmaking techniques particularly with respect to control of nitrogen content. The standard austenitic stainless steel like 304 (1.4301) and ferritic stainless steel like 430 are relatively easy to make and to fabricate. As their names imply, they consist mainly of one phase, austenite or ferrite. Although these types are fine for a wide range of applications, there are some important technical weaknesses in both types: Austenitic stainless steel– low strength (200 MPa 0.2% PS in solution annealed condition), low resistance to stress corrosion cracking Ferritic stainless steel– low strength (a bit higher than austenitic, 250 MPa 0.2% PS), poor weldability in thick sections, poor lowtemperature toughness In addition, the high nickel content of the austenitic stainless steel types leads to price volatility which is unwelcome to many end users. The basic idea of duplex stainless steel is to produce a chemical composition that leads to an approximately equal mixture of ferrite and austenite. This balance of phases provides the following: Higher strength – The range of 0.2% PS for the current duplex stainless steel grades is from 400 – 550 MPa. This can lead to reduced section thicknesses and therefore to reduced weight. This advantage is particularly significant for applications such as:  o Pressure Vessel and Storage Tanks o Structural Applications e.g. bridges Good weldability in thick sections – Not as straightforward as austenitics but much better than ferritics. Good toughness – Much better than ferritics particularly at low temperature, typically down to minus 50 deg C, stretching to minus 80 deg C. Resistance to stress corrosion cracking – Standard austenitic stainless steels are particularly prone to this type of corrosion. The kind of applications where this advantage is important include:  o Hot water tanks  o Brewing tanks  o Process plant  o Swimming pool structures

The first-generation duplex stainless steel were developed more than 70 years ago in Sweden for use in the sulfite paper industry. Duplex alloy were originally created to combat corrosion problem caused by chloride-bearing cooling water and other aggressive chemical process fluid. Called duplex because of its mixed microstructure with about equal proportion of ferritic andaustenitic. Duplex stainless steel are a family of grade, which corrosion performance depending on their alloy content.  ​ The term “Super-Duplex” was first used in the 1980’s to denote highly alloyed, high-performance Duplex stainless steel with a pitting resistance equivalent of >40 (based on Cr% + 3.3Mo% + 16N%). With its high level of chromium, Super duplex stainless steel provides outstanding resistance to acids, acid chlorides, caustic solutions and other environments in the chemical / petrochemical, pulp and paper industries, often replacing 300 series stainless steel, high nickel super-austenitic stainless steel and nickel based alloys. The chemical composition based on high contents of chromium, nickel and molybdenum improves intergranular and pitting corrosion resistance. Additions of nitrogen promote structural hardening by interstitial solid solution mechanism, which raises the yield strength and ultimate strength values without impairing toughness. Moreover, the two-phase microstructure guarantees higher resistance to pitting and stress corrosion cracking in comparison with conventiona stainless steel. From the introduction of its first-generation, Duplex steel has seen a steady increase in popularity. Recently, the production of high-strength, corrosion resistant super-duplex coil has been implemented in the marine and chemical industries, architecture and mast riggings, wire lines, lifting and pulley equipment and well service strands. In fact, development of wire processing techniques has enabled the production of steel wires down to 1mm in diameter.  The various Alloys Super-Duplex falls under the Duplex stainless steel grouping. Duplex stainless steel are graded for their corrosion performance depending on their alloy content. Today, modern Duplex stainless steel can be pided into four groups: Lean Duplex such as 2304, which contains no deliberate Mo addition; 2205, the work-horse grade accounting for more than 80% of duplex usage; 25 Cr duplex such as Alloy 255 and DP-3; Super-Duplex; with 25-26 Cr and increased Mo and N compared with 25 Cr grades, including grades such as 2507, Zeron 100, UR 52N+, and DP-3W Composition of Duplex Stainless Steel The table lists the duplex stainless steel covered in ASTM specifications for plate, sheet, and bar products.UNS Number  Duplex GradesTypebCMnPSSiCrNiMoNCuOtherS31200…0.0302.000.0450.0301.0024.0-26.05.5-6.51.20-2.000.14-0.20……S31260…0.031.000.0300.0300.7524.0-26.05.5-7.52.5-3.50.10-0.200.20-0.80W0.10-0.20S31803…0.0302.000.0300.0201.0021.0-23.04.5-6.52.5-3.50.08-0.20… S32001…0.0304.0-6.00.0400.0301.0022.0-23.01.00-3.000.600.05-0.171.00 S3220522050.0302.000.0300.0201.0019.5-21.54.5-6.53.0-3.50.14-0.20… S3230423040.0302.500.0400.0301.0021.5-24.53.0-5.50.05-0.600.05-0.200.05-0.60 S32520…0.0301.500.0350.0200.8024.0-26.05.5-8.03.0-4.00.20-0.350.50-2.00 S325502550.041.500.0400.0301.0024.0-27.04.5-6.52.9-3.90.10-0.251.5-2.5 S3275025070.0301.200.0350.0200.8024.0-26.06.0-8.03.0-5.00.24-0.320.50 S32760…0.0301.000.0300.0101.0024.0-26.06.0-8.03.0-4.00.20-0.300.50-1.00cS32900329d0.061.000.0400.0300.7523.0-28.02.5-5.01.0-2.0…… S32950…0.032.000.035 a Weight percent, maximum unless otherwise noted.  b Unless otherwise indicated, a common name, not a trademark, widely used, not associated with any one producer, as listed in ASTM A 240.  c W 0.50-1.00; Cr+3.3Mo+16N=40 min.  d AISI designation BENEFITS High strength, High resistance to pitting, crevice corrosion resistance. High resistance to stress corrosion cracking, corrosion fatigue and erosion, Excellent resistance to chloride stress-corrosion cracking High thermal conductivity Low coefficient of thermal expansion Good sulfide stress corrosion resistance, Low thermal expansion and higher heat conductivity than austenitic steels, Good workability and weldability, High energy absorption. Applications Duplex Stainless Steel Pipes and duplex Stainless Steel tubes for production and handling of gas and oil, Heat exchanger and duplex Stainless Steel pipes in desalination plants, Mechanical and structural components, Power industry FGD systems, Duplex Stainless Steel pipes in process industries handling solutions containing chlorides, Utility and industrial systems, rotors, fans, shafts and press rolls where the high corrosion fatigue strength can be utilized, Cargo tanks, vessels, piping and welding consumables for chemical tankers. High-strength, highly resistant wiring. Seamless Duplex Stainless Steel Pipes 1. ASTM A789/A789M 12.7-1016x 0.5-25.4mm  2. ASTM A790/A790M 10.3-1016x 0.5-36mm 3. API 6L  EFW Duplex Stainless Steel Pipes  1.ASTM A789/A789M:12.7-323.9×0.5-12.7mm  2:ASTM A790/A790M 10.3-610×0.5-18mm  3.ASTM A928/A928M 10.3–610x 0.5-18mm  Material: UNS S31500 S32304 S31803 S2205 S2760 S2750,S 32205, S 32550, S32750, S 32760.Specifications:Seamless Duplex Stainless Steel Pipes 1. ASTM A789/A789M 12.7-1016x 0.5-25.4mm 2. ASTM A790/A790M 10.3-1016x 0.5-36mm  EFW Duplex Stainless Steel Pipes 1.ASTM A789/A789M:12.7-323.9×0.5-12.7mm 2:ASTM A790/A790M 10.3-610×0.5-18mm 3.ASTM A928/A928M 10.3-610x 0.5-18mm Material: UNS S31500 S32304 S31803 S2205 S2760 S2750,S 32205, S 32550, S 32750, S 32760. Duplex Stainless Steel have a structure that contains both ferrite and austenite. Duplex alloys have higher strength and better stress corrosion cracking resistance than most austenitic alloys and greater toughness than ferritic alloys, especially at low temperatures. The corrosion resistance of duplex alloys depends primarily on their composition, especially the amount of chromium, molybdenum, and nitrogen they contain. Duplex alloys are often pided into three sub-classes: Lean Duplex (AL 2003 alloy), Standard Duplex (AL 2205 alloy), and Superduplex (AL 255 Alloy and UNS S32760).Standard Met: Duplex Stainless Steels: Part One Abstract:  Stainless steel is the name given to a family of corrosion and heat resistant steels containing a minimum of 10.5% chromium. Just as there is a range of structural and engineering carbon steels meeting different requirements of strength, weldability and toughness, so there is a wide range of stainless steels with progressively higher levels of corrosion resistance and strength.  Duplex stainless steels have a mixture of austenitic and ferritic grains in their microstructure; hence they have a duplex structure. This effect is achieved by adding less nickel than would be necessary for making a fully austenitic stainless steel. Microstructure Stainless steel is the name given to a family of corrosion and heat resistant steels containing a minimum of 10.5% chromium. Just as there is a range of structural and engineering carbon steels meeting different requirements of strength, weldability and toughness, so there is a wide range of stainless steels with progressively higher levels of corrosion resistance and strength. This results from the controlled addition of alloying elements, each offering specific attributes in respect of strength and ability to resist different environments. The available grades of stainless steel can be classified into five basic families: ferritic, martensitic, austenitic, duplex and precipitation hardenable.  The pision based on microstructure is useful because the members within one family tend to have similar physical and mechanical properties. However, the properties for one family can be very different from the properties for another family. For example, austenitic stainless steels are non-magnetic, while ferritic and duplex stainless steels are magnetic.  The difference between the families is fundamental on the atomic level. The arrangement of atoms in the ferrite crystal is different from the one in the austenite crystal:  Figure 1: The ferritic stainless steel on the left has a body centered cubic (bcc) crystal structure. By adding nickel to this stainless steel the structure changes from bcc to face centered cubic (fcc), which is called austenitic. In the ferritic stainless steel, the iron and chromium atoms are arranged on the corners of a cube and in the center of that cube. In the austenitic stainless steels the atoms, here iron, chromium and nickel, are arranged on the corners of the cube and in the center of each of the faces of the cube. This seemingly small difference profoundly affects the properties of these steels.  Table 1: Select properties of austenitic and ferritic stainless steels Properties Austenitic Ferritic  Toughness Very high Moderate  Ductility Very high Moderate  Weldability Good Limited  Thermal expansion High Moderate  Stress corrosion cracking resistance Low Very high  Magnetic properties Non-magnetic Ferro magnetic  Because of their good mechanical properties and the ease of fabrication, austenitic stainless steels are much more widely used than ferritic stainless steels. About 75% of all stainless steel used worldwide is austenitic and about 25% is ferritic. The other families, martensitic, duplex and precipitation hardenable stainless steels each represent less than 1% of the total market.  Besides nickel there are other elements that tend to make the structure austenitic. These elements are called austenite formers. Alloying elements that tend to make the structure ferritic are called ferrite formers.  Table 2: Alloying elements formers for stainless steel microstructure Ferrite formers Austenite formers  Iron Nickel  Chromium Nitrogen  Molybdenum Carbon  Silicon Manganese  Copper Duplex stainless steels have a mixture of austenitic and ferritic grains in their microstructure; hence they have a duplex structure. This effect is achieved by adding less nickel than would be necessary for making a fully austenitic stainless steel.  Figure 2: Adding 8% nickel to a ferritic chromium stainless steel makes an austenitic chromium-nickel stainless steel, for example Type 304 stainless steel. If less nickel is added to a chromium steel, about four or five percent, a duplex structure, a mixture of austenite and ferrite, is created as in 2205 duplex stainless steel.  Austenitic-ferritic (Duplex) stainless steels contain increased amount of chromium (18% -28%) and decreased (as compared to austenitic steels) amount of nickel (4.5% – 8%) as major alloying elements. As additional alloying element molybdenum is used in some of Duplex steels. Since the quantity of nickel is insufficient for formation of fully austenitic structure, the structure of Duplex steels is mixed: austenitic-ferritic.  The properties of Duplex steels are somewhere between the properties of austenitic and ferritic steels. Duplex steels have high resistance to the stress corrosion cracking and to chloride ions attack. These steels are weldable and formable and possess high strength  In the annealed condition, most wrought duplex stainless steels contain about 40-50% austenite in a ferritematrix. When these materials solidify, σ ferrite forms first. Depending upon the composition, a varying amount of austenite is expected to form as the last material solidifies.  Additional austenite forms by a solid-phase transformation during subsequent annealing. Accordingly, an annealed product is expected to contain more austenite than as-cast or as-welded material. A sufficient amount of austenite must be maintained to provide satisfactory corrosion resistance and mechanical properties. This amount of austenite may vary with the service application and with alloy composition and thermal history.  Additional phases found in duplex stainless steels can include σ, χ, R, α’, carbides and nitrides. These phases have generally been studied using isothermal heat treatments in the laboratory.  Sigma Phase Sigma is a hard, brittle intermetallic phase which is expected to contain iron, chromium and molybdenum in most duplex stainless steels. In these alloys, σ generally can be formed between about 600 and 950°C, with the most rapid formation occurring between 700 and 900°C.  Sigma typically nucleates in the austenite-ferrite grain boundaries and grows into the adjacent ferrite. Often, additional austenite forms in the areas of chromium depletion adjacent to the σ phase. Elements which stabilize ferrite such as chromium, molybdenum and silicon increase the tendency to form the σ phase. On a weight percent basis, molybdenum can promote σ phase formation much more effectively than chromium, particularly at higher temperatures (e.g. about 900°C). Austenite forming elements such as nickel or nitrogen can also accelerate the nucleation and growth of the σ phase, although these elements may reduce the total amount formed.  The alloy elements are portioned, and increased levels of each element tend to be present in the phases they stabilize. As nickel or nitrogen stabilize additional austenite, the reduced amount of ferrite becomes enriched in chromium and molybdenum. As a result, σ phase formed may be reduced by nickel or nitrogen, however, because of the smaller volume fraction of ferrite.  The σ phase can deplete chromium and molybdenum in surrounding areas and reduce resistance to corrosion. As little as about 1% σ phase may reduce impact toughness, while about 10% can cause complete embrittlement of duplex stainless steels.

SCC Stress Corrosion Cracking Of Duplex Stainless Steel is a form of corrosion which occurs with a particular combination of factors: Tensile stress Corrosive environment Sufficiently high temperature. Normally 50 deg C but can occur at lower temperatures around 25 deg C in specific environments, notably swimming pools. Unfortunately, the standard austenitic stainless steel like 304 (1.4301) and 316 (1.4401) are the most susceptible to SCC. The following materials are much less prone to SCC: Ferritic stainless steel Duplex stainless steel High nickel austenitic stainless steel The resistance to SCC makes duplex stainless steels suitable materials for many processes which operate at higher temperature, notably: Hot water boilers Brewing tanks Desalination Stainless steel structures in swimming pools are known to be prone to SCC. The use of standard austenitic stainless steel like 304 and 316 is forbidden in this application. The best stainless steels to use for this purpose are the high nickel austenitic stainless steel such as the 6% Mo grades. However, in some cases, duplex steel such as S32205 (1.4462) and the superduplex stainless steel grades can be considered.

The range of duplex stainless steel allows them to be matched for corrosion resistance with the austenitic stainless steel and ferritic stainless steel grades. There is no single measure of corrosion resistance. However, it is convenient to use the Pitting Resistance Equivalent Number (PREN) as a means of ranking the grades.  PREN = %Cr + 3.3 x %Mo + 16 x %N  The following table shows how the duplex stainless steel compare with some austenitic stainless steel and ferritic stainless steel grades. GradeEN No/UNSTypeTypical PREN4301.4016/  S43000Ferritic stainless steel183041.4301/  S30400Austenitic stainless steel 194411.4509/  S43932Ferritic stainless steel19RDN 9031.4482/  S32001Duplex stainless steel 22316 1.4401/ S31600Austenitic stainless steel 244441.4521/  S44400Ferritic stainless steel24  316L 2.5 Mo1.4435Austenitic stainless steel 262101 LDX 1.4162/ S32101Duplex stainless steel2623041.4362/  S32304Duplex stainless steel26DX22021.4062/ S32202Duplex stainless steel27  904L1.4539/  N08904Austenitic stainless steel342205 1.4462/ S31803/ S32205Duplex stainless steel35Zeron 100 1.4501/ S32760Duplex stainless steel41Ferrinox 255/  Uranus 2507Cu1.4507/  S32520/ S32550Duplex stainless steel 4125071.4410/  S32750Duplex stainless steel436% Mo1.4547/  S31254Austenitic stainless steel44 It must be emphasised that this table is only a guide to material selection. It is always important to assess the suitability of a particular with a full knowledge of the corrosive environment.

The attractive combination of high strength, wide range of corrosion resistance, moderate weldability would seem to offer great potential for increasing the market share of duplex stainless steel. However, it is important to understand the limitations of duplex stainless steel and why they are always likely to be “niche players”.  The advantage of high strength immediately becomes a disadvantage when considering formability and machinability. The high strength also comes with lower ductility than austenitic stainless steel grades. Therefore, any application requiring a high degree of formability, for example, a sink, is ruled out for duplex stainless steel grades. Even when the ductility is adequate, higher forces are required to form the material, for example in tube bending. There is one exception to the normal rule of poorer machinability, grade 1.4162. The metallurgy of duplex stainless steel is much more complex than for austenitic or ferritic steel. This is why 3 day conferences can be devoted just to duplex! This factor means that they are more difficult to produce at the mill and to fabricate.  In addition to ferrite and austenite, duplex stainless steel can also form a number of unwanted phases if the stainless steel is not given the correct processing, notably in heat treatment.  Two of the most important phases are illustrated in the diagram below: Sigma phase Both of these phases lead to embrittlement, i.e. loss of impact toughness.  The formation of sigma phase is most likely to occur when the cooling rate during manufacture or welding is not fast enough. The more highly alloyed the stainless steel, the higher the probability of sigma phase formation. Therefore, superduplex stainless steels are most prone to this problem.  475 degree embrittlement is due to the formation of a phase called α′ (alpha prime). Although the worst temperature is 475 deg C, it can still form at temperatures as low as 300 deg C. This leads to a limitation on the maximum service temperature for duplexstainless steel. This restriction reduces the potential range of applications even further. At the other end of the scale, there is a restriction on the low temperature use of duplex stainless steel compared to austenitic grades. Unlike austenitic stainless steel, duplex stainless steel exhibit a ductile-brittle transition in the impact test. A typical test temperature is minus 46 deg C for offshore oil and gas applications. Minus 80 deg C is the lowest temperature that is normally encountered for duplex stainless steel. Source: wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

The Duplex Stainless Steel Grades Comparison Table is intended to relate former BS, EN, German and Swedish grade designations to the current EN duplex stainless steel numbers, AISI grades and UNS (Unified Numbering System) numbers. The table is based on the ‘wrought’ ie long products (duplex stainless steel pipes etc), pipe fitting products (duplex stainless steel eccentric reducer, etc), duplex stainless steel numbers published in EN 10088 and related standards.  Castings products use different compositions and so have their own duplex stainless steel numbers in EN 10283. The related castings grades in both EN 10283 and BS 3100 are included in the table. The ‘Chemical Composition’ is intended to represent the composition only. This does not show the specified or typical composition of commercially available duplex stainless steels. Specified ranges for the wrought European grades can be found in either the EN 10088-2 or EN10088-3 tables. None of the duplex stainless steels listed were included in either BS 970 or BS 1449. The castings grades specified ranges can be found in the EN 10283 or BS 3100 tables. These are comparisons only and cannot be assumed to be direct equivalent grades. The data given is not intended to replace that shown in inpidual standards to which reference should always be made. Duplex Stainless Steel Grades table EN 10088Common NamesBS WroughtAISIUNSEnGerman DINSSEN 10283BS CastChemical Composition..........CCrNiMoOthers1.4162LDX 2101––S32101–––––0.030x21.51.50.35Mn1.4362SAF2304/UR35N––S32304–X2CrNiN23-42327––0.030x2240.40.4Cu1.4410SAF2507 /UR47N/F53––S32750––23281.4468–0.030x2463–1.4460453S–329S32900–X4CrNiMoN27-5-22324––0.05x2551.5–1.4462SAF2205/Falc223 /UR45N/F51318S13–S31803 S32205–X2CrNiMoN22-5-323771.4470332C150.030x2253–1.4501Zeron 100/F55––S32760–––1.4417–0.030x24630.5W1.4507Ferralium 255 /UR52N/F61––S32550–––––0.030x24631Cu Note Chemical composition figures are intended to be representative of the grade, not typical. ‘x’ indicates a maximum Source: wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

Duplex Stainless Steel 2205 S32205 S31803 is a 22% chromium, 3% molybdenum, 5-6% nickel, nitrogen alloyed duplex stainless steel with high general, localized, and stress corrosion resistance properties in addition to high strength and excellent impact toughness. Duplex Stainless Steel 2205 S32205 S31803 provides pitting and crevice corrosion resistance superior to 316L or 317L austenitic stainless steel in almost all corrosive media. It also has high corrosion and erosion fatigue properties as well as lower thermal expansion and higher thermal conductivity than austenitic.The advantage of a duplex structure is that it combines the favorable qualities of aferritic alloy stress corrosion cracking resistance and high strength with austenitic alloy ease of fabrication and corrosion resistance. Duplex Stainless Steel 2205 S32205 S31803 is a nitrogen enhanced duplex stainless steel that was developed to combat common corrosion problems encountered with the 300 series stainless steel. “Duplex” describes a family of stainless steel that are neither fully austenitic, like 304 stainless steel, nor purely ferritic, like 430 stainless steel. The structure of 2205 duplex stainless steel consists of austenitic pools surrounded by a continuous ferritic phase. In the annealing condition, 2205 contains approximately 40-50% ferrite. Often referred to as the work horse grade, 2205 is the most widely used grade in the duplex stainless steel tube. Usage of Duplex stainless steel 2205 should be limited to temperatures below 600° F.  Extended elevated temperatureexposure can embrittle 2205 stainless. 1.4462 Composition % according to EN-10216-5:CSiMnPSCrMoNiNCumax. 0,03max. 1,00max. 2,00max. 0,035max. 0,01521,00 – 23,002,50 – 3,504,50 – 6,500,10-0,22– S32205 Composition % according to ASTM A789 ASTM A790:CSiMnPSCrMoNiNCumax. 0,03max. 1,00max. 2,00max. 0,030max. 0,02022,00 – 23,003,0 – 3,54,5 – 6,500,14-0,20– S31803 Composition % according to ASTM A789 ASTM A790:CSiMnPSCrMoNiNCumax. 0,03max. 1,00max. 2,00max. 0,030max. 0,02021,00 – 23,002,5 – 3,54,50 – 6,500,08-0,20– General Properties Application Standards Chemical Composition Resistance to Corrosion Physical Properties Mechanical Properties Structure Welding Processing Machinability Duplex Stainless Steel 2205 Product InformationProductsODWallLengths and/or coilsGradesODWallLengths 3/16″ (4.76 mm) to 4″ (101.6 mm)Metric sizes available0.020″ (0.51 mm) to 0.220″ (5.59 mm)Random or cut lengths up to 68′ (20.7 m) Coils to 1-1/2″ ODDuplex 2205 <1-1/2" (38.1 mm) ±0.005" (0.13 mm) 1-1/2″ (38.1 mm) to 3″ (76.2 mm) ±0.010″ (0.25 mm) 3-1/2″ (88.9 mm) to 4″ (101.6 mm) ±0.015″ (0.38 mm)±10%Randoms up to +2″ (50.8 mm) Cuts +1/8″ (3 mm) -0″ Coils to 80,000′ (24,384 m) Physical Properties of Duplex Stainless Steel Alloys in the Annealed Condition at -20°F to +100°F Tensile StrengthYield Strength AlloyUNS DesignationSpec.psiMPaksipsiMPaksiElongation in 2 in. (min.) %Grain SizeReq.Max. HardnessModulus of Elasticity(x106 psi)Mean Coefficient of Thermal Expansion (IN./IN./°F x 10-6)Thermal Conductivity (BTU-in/ ft2-h-°F)Duplex 2205S32205A789,A79095,0006559570,0004857030—28 Rc, 30* Rc27.57.6180Duplex 2205S31803A789, A79090,0006209565,0004507030—28 Rc, 30* Rc27.57.6180 *OD over 1.0″ TS>87, YS>58, no hardness requirement 1.0″ OD and under Duplex Stainless Steel Product RangeAlloyUNS DesignationWerkstoff NR.Specifications*Duplex 2205S31803/S322051.4462A/SA789, A/SA790 *Note: The specifications noted including ASTM, ASME, or other applicable authorities are correct at the time of publication. Other specifications may apply for use of these materials in different applications.

LDX 2101 UNS S32101 is a lean duplex stainless steel designed for general purpose use. LDX 2101 UNS S32101 is a 21.5% chromium, 5% manganese, 1.5% nickel, 0.45% molybdenum lean duplex stainless steel with corrosion resistance superior to 304L stainless steel and comparable to 316L stainless steel. LDX 2101 UNS S32101 Duplex Stainless Steel is a low-alloyed, general purpose lean duplex stainless steel. It possesses properties such as high mechanical strength, similar to that of other duplex stainless steel, and good corrosion resistance. Compared to 300 series stainless steels, 2101 duplex stainless steel provides superior strength and greater chloride stress corrosion cracking resistance. The use of manganese ensures proper ferrite-austenite phase balance, while allowing a reduction in nickel content. As a result, LDX 2101 UNS S32101 Duplex Stainless Steel is priced competitively with 304L stainless steel and 316L stainless steel.  Due to its relatively low alloying content, it is less prone to precipitation of intermetallic phases than other duplex stainless steel. Corrosion Resistance The corrosion resistance of LDX 2101 uns s32101 duplex stainless steel is generally good, and therefore is suitable for use in a wide range of general-purpose applications and environments. Attributable to its duplex structure, LDX 2101 uns s32101 duplex stainless steel offers an excellent resistance to stress corrosion cracking. It also offers corrosion resistance comparable to 304L and 316L stainless steel, making it an excellent candidate to replace 300 series stainless in a wide variety of applications. What are the characteristics of LDX 2101 uns s32101 duplex stainless steel? High resistance to chloride stress corrosion cracking Chloride pitting and crevice corrosion resistance comparable to 316L stainless steel Good general corrosion resistance High strength Good sulfide stress corrosion resistance Good machinability and weldability Chemical Composition, % CrNiMoCNMn21.0-22.01.35-1.700.10-0.80.040 Max0.20-0.254.00-6.00SiPSCuFe 1.00 Max.040 Max.030 Max0.10-0.80Balance In what applications is LDX 2101 uns s32101 duplex stainless steel used? Chemical process vessels, piping and heat exchanger General purpose stainless steel applications Storage Tanks Water treatment Pulp & Paper mill equipment Water heater tanks LDX 2101 UNS S32101 Duplex Stainless Steel Pipe ASTM Specifications Pipe SmlsWelded PipeTube SmlsTube WeldedSheet/PlateBarA790A790A789A789A240A276 Mechanical Properties Of UNS S32101 Duplex Stainless Steel Pipe Specified Tensile Properties ASTM A240 Cold Rolled Plate and Sheet > ¼” AlloyUltimate Tensile Strength, ksi Minimum.2% Yield Strength, ksi MinimumElongation % MinimumHardness Brinell Maximum2101946530290304/304L753040201316/316L7530402172205956525293 Mechanical Properties Of UNS S32101 Duplex Stainless Steel Pipe Specified Tensile Properties ASTM A240 Cold Rolled Plate and Sheet ≤ ¼”AlloyUltimate Tensile Strength, ksi Minimum.2% Yield Strength, ksi MinimumElongation % MinimumHardness BrinellMaximum21011017730290304/304L753040201316/316L7530402172205956525293 LDX 2101 UNS S32101 Duplex Stainless Steel is a registered trademark of Outokumpu Stainless Steel. Physical Properties Density: 0.278 lb/inch3  Melting Point: 2525- 2630°F Poisson’s Ratio: 0.3  Electrical Resistivity: 481 Ohm – circ mil/ftTemperature, °F70212392572Coefficient* of Thermal Expansion, in/in°F x 10-6–7.57.88.1Thermal Conductivity Btu • ft/ft2 • hr • °F9.29.811.011.6Modulus of Elasticity, Dynamic psi x 10629.72927.626.1 * 70°F to indicated temperature. Source: wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)